Person: Košmrlj, Andrej
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Košmrlj
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Andrej
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Košmrlj, Andrej
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Publication A monomer-trimer model supports intermittent glucagon fibril growth(Nature Publishing Group, 2015) Košmrlj, Andrej; Cordsen, Pia; Kyrsting, Anders; Otzen, Daniel E.; Oddershede, Lene B.; Jensen, Mogens H.We investigate in vitro fibrillation kinetics of the hormone peptide glucagon at various concentrations using confocal microscopy and determine the glucagon fibril persistence length 60μm. At all concentrations we observe that periods of individual fibril growth are interrupted by periods of stasis. The growth probability is large at high and low concentrations and is reduced for intermediate glucagon concentrations. To explain this behavior we propose a simple model, where fibrils come in two forms, one built entirely from glucagon monomers and one entirely from glucagon trimers. The opposite building blocks act as fibril growth blockers, and this generic model reproduces experimental behavior well.Publication Complex Ordered Patterns in Mechanical Instability Induced Geometrically Frustrated Triangular Cellular Structures(American Physical Society, 2014) Kang, Sung; Shan, Sicong; Košmrlj, Andrej; Noorduin, Wim L.; Shian, Samuel; Weaver, James; Clarke, David; Bertoldi, KatiaGeometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.Publication Thermal Excitations of Warped Membranes(American Physical Society, 2014) Košmrlj, Andrej; Nelson, DavidWe explore thermal fluctuations of thin planar membranes with a frozen spatially varying background metric and a shear modulus. We focus on a special class of D-dimensional “warped membranes” embedded in a d-dimensional space with d≥D+1 and a preferred height profile characterized by quenched random Gaussian variables \(\{h_\alpha(q)\}\), \(\alpha=D+1,...,d\), in Fourier space with zero mean and a power-law variance \(\over{h\alpha(q_1)h_\beta(q_2)}\) \(\sim \delta_{\alpha,\beta} \delta_{q_1,−q_2} q_1^{-d_h}\). The case D=2, d=3, with \(d_h=4\) could be realized by flash-polymerizing lyotropic smectic liquid crystals. For \(D\lt max\{4,d_h\}\) the elastic constants are nontrivially renormalized and become scale dependent. Via a self-consistent screening approximation we find that the renormalized bending rigidity increases for small wave vectors q as \(\kappa_R \sim q^{−\eta_f}\), while the in-hyperplane elastic constants decrease according to \(\lambda_R, \mu_R \sim q^{+\eta_u}\). The quenched background metric is relevant (irrelevant) for warped membranes characterized by exponent \(d_h\gt 4−\eta^{(F)}_f (d_h\lt 4−\eta ^{(F)}_f)\), where \(\eta^{(F)}_f\) is the scaling exponent for tethered surfaces with a flat background metric, and the scaling exponents are related through \(\eta_u+\eta_f=d_h−D (\eta_u+2\eta_f=4−D)\).Publication Mechanical Properties of Warped Membranes(American Physical Society, 2013) Košmrlj, Andrej; Nelson, DavidWe explore how a frozen background metric affects the mechanical properties of planar membranes with a shear modulus. We focus on a special class of “warped membranes” with a preferred random height profile characterized by random Gaussian variables h(q) in Fourier space with zero mean and variance \(⟨| h(q)|^2〉\sim q^{−d_h}\) and show that in the linear response regime the mechanical properties depend dramatically on the system size L for \(d_h\geq 2\). Membranes with \(d_h=4\) could be produced by flash polymerization of lyotropic smectic liquid crystals. Via a self-consistent screening approximation we find that the renormalized bending rigidity increases as \(\kappa R\sim L^{(d_h−2)/2}\) for membranes of size L, while the Young and shear moduli decrease according to \(Y_R,\mu R \sim L^{−(d_h−2)/2}\) resulting in a universal Poisson ratio. Numerical results show good agreement with analytically determined exponents.